13C NMR studies and orientational order of rod-like mesogens with strongly polar terminal cyano group

Kesava Reddy, M and Santhosh Kumar Reddy, Y and Lobo, NP and Ramanathan, KV and Narasimhaswamy, T (2024) 13C NMR studies and orientational order of rod-like mesogens with strongly polar terminal cyano group. In: Liquid Crystals .

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Abstract

13C NMR studies of two rod-like mesogens with core units consisting of two and three phenyl rings with strongly polar terminal cyano groups are reported. The two-ring mesogen displayed an enantiotropic smectic A (SmA) mesophase while for the three-ring mesogen, enantiotropic nematic and SmA mesophases were observed. The solution 13C NMR studies of both the mesogens are carried out besides static 13C NMR measurements in the liquid crystalline phase. For the two-ring mesogen, the chemical shift anisotropy (CSA) tensors of the core unit are determined by the 2D-separation of undistorted powder patterns by effortless recoupling (SUPER) experiment. Furthermore, 2D-separated local field (SLF) measurements are realised for both the mesogens in the liquid crystalline phase to determine the 13C-1H dipolar couplings to find the orientational order parameters of the phenyl rings. The main order parameter (Szz) of the two-ring mesogen varies from 0.63 to 0.53 across the SmA phase and for the three-ring mesogen, the Szz values are found to be ~0.73 in the SmA phase and ~0.69 in the nematic phase. The CSA values determined from the SUPER experiment are expected to be a significant utility for molecules with polar terminal nitro/cyano groups as ferroelectric nematic phases are realised in them. © 2024 Informa UK Limited, trading as Taylor & Francis Group.

Item Type:	Journal Article
Publication:	Liquid Crystals
Publisher:	Taylor and Francis Ltd.
Additional Information:	The copyright for this article belongs to Taylor and Francis Ltd.
Department/Centre:	Division of Chemical Sciences > NMR Research Centre (Formerly Sophisticated Instruments Facility)
Date Deposited:	09 Dec 2024 17:44
Last Modified:	09 Dec 2024 17:44
URI:	http://eprints.iisc.ac.in/id/eprint/87078

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